This invention is concerned with dentifrice abrasives. In particular, it involves an improved silica abrasive.
Modern dentifrice compositions contain numerous components that have various therapeutic and cosmetic functions. Most of these compositions contain an abrasive cleansing agent which aids in the removal of adherent deposits on the teeth. Particulate matter of specific hardness and certain particle size, shape and structure are utilized as such abrasives. These particles must also be compatible with other toothpaste ingredients and safe for repeated human use. Abrasives that are described in the patent literature and have found commercial application include silica xerogels, hydrated silicas, hydrated aluminas, calcium carbonate, dicalcium phosphate (anhydrous and dihydrate), calcium pyrophosphate, and insoluble sodium metaphosphate. These agents are usually 2 to 30 micrometers (.mu.m) in size. Products of about 10 .mu.m appear to find the most commercial acceptance. Insoluble crystalline materials such as quartz have been found too abrasive for safe use on human teeth.
The use of silica xerogels is described in U.S. Pat. No. 3,538,230 to Pader & Weisner. This patent teaches that hydrogels prepared by acidifying a sodium silicate solution and then dried to a water content of 0.6 to 6% provide a xerogel that can be used as an abrasive especially for translucent and transparent toothpastes. U.S. Pat. No. 4,153,680 to Seybert teaches the use of a hydrogel as an abrasive for a dentifrice. This patent discloses that hydrogels prepared by neutralizing a sodium silicate solution and dried to between 17 and 32% water are effective abrasives. An important teaching of this patent is that the gel cannot be dried significantly below the level desired and then rehydrated to produce an effective product.